Microwave devices utilizing eu-fe garnet containing ga



DeC- 5, 1967 R. c. LE cRAw ETAL 3,356,929

MICROWAVE DEVICES UTILIZING EUFS GARNET CONTAINING GCI.

5 Sheets-Sheet 1 Filed JulyA l, 1964 ooof A. C. LE CRAW /Nl/E/v Tops H.MA 7 THE W5 By J. F. HEME/KA A TTONE V Dec. 5, 1967 R. c. LE cRAw ETAL3,356,929

MICROWAVE DEVICES UTILIZING Ell-Fe GARNET CONTAINING G11 Filed July 1,1964 Y 5 sheets-sheet 2 Dec. 5, 1967 R, Q LE RAW ETAL 3,356,929

MICROWAVE DEVICES UTILIZING Eu-Fe GARNET CONTAINING GG Filed July 1,1964 3 Sheets-Sheet s' United States Patent O 3,356,929 MICRGll/AVEDEVICES UTILIZING E11-Fe CARNET CONTAINING Ga Roy C. Le Eraw and HerbertMatthews, Madison, and

.loseph l. Remeilra, Warren Township, Somerset County, NJ., assignors toBell Telephone Laboratories, Incorporated, New York, NEI., a corporationot New York Filed Juiy fr, 1964, Ser. No. 379,586 7 Ciaims. (Cl. 321-69)This invention relates to magnetic compositions of matter useful as theactive elements in microwave devices and to devices constructed of suchmaterial. It is the nature of these materials and related devices thatthey are useful over a frequency range extending well above 50gigacycles per second.

Microwave technology has reached a high state of development over thepast decade, Commercial circuitry, particularly in communications,utilizes a vast array of circuit elements for controlling energy oversuch frequency range. A large family of these devices, includingisolators based on rotation, absorption, and tield displacementcirculators, phase Shifters, switches, frequency multipliers, etc., makeuse of magnetic materials biased to saturation and beyond.

It is well known that the frequency capability of this class of devicesis directly dependent on the gyromagnetic activity of the material,coupled with the line width. For most of these devices, line width isdesirably narrow to premit operation close to resonance withoutincurring the large associated absorption loss.

The relationship ,between frequency capability and gyromagnetic activityis discussed in the description of the frequency multiplier, in whichoperation depends on biasing to a resonance point set by the fundamentalfrequency to be introduced into the device.

Operation of any of the above devices to frequencies of the order of asmall number of gigacycles per second is feasible for many of thecommonly used ferrite or garnet materials. Most of these manifestgyromagnetic ratios of approximately 2.8 megacycles per second peroersted, so permitting operation at gigacycles per second, with appliedfields of the order of 1.5 kilo-oersteds. Fields of this order aregenerally available from simple solenoids and even by 'use of carefullydesigned, shaped pole permanent magnets. Operation at significantlyhigher frequencies, however, requires the use of biasing fields of 10kilo-oersteds or higher. Such field values are inconveniently large formost purposes.

The essence of the instant invention is the discovery of the unusuallyhigh gyromagnetic ratios in a specilic range of magnetic garnetcompositions. The compositional range is conveniently dened in atomicunits as in which x is from 0.8 to 1.8. Magnetic, chemicals, andphysical properties of this material are suitable for device use.Claimed embodiments of the invention include the devices set forthabove, operation of which is dependent upon crystalline bodies of thespecified composition.

Description of the invention is facilitated by reference to thedrawings, in which:

FIG, 1, on coordinates of saturation moment on the ordinate and x in thegeneral formula Eu3GaXFe5 XO12 on the abscissa, is a plot of thedependence of this magnetic property on composition;

FIG. 2, in units of gyromagnetic ratio on the ordinate and x on theabscissa, is a plot showing the interdependence of these properties,clearly delineating the composition region for angular momentumcompensation;

3,356,929 Patented Dec. 5,Y 1967 ICS FIG. 3 is a plot of cubicanisotropy constant on the ordinate against x on the abscissa;

FIG. 4 is a perspective View of a frequency doubling configuration,operation of which is based on the inclusion of an element of acomposition of this invention;

FIG. 5 is a perspective view, partly in section, of a Faraday rotationtype of circulator mounted in a hollow metallic waveguide utilizing anelement of a composition herein;

FIG. 6 is -a perspective View, partly in section, of a round dielectricwaveguide containing a garnet composition of this invention forproducing Faraday rotation;

FIG. 7 is a perspective view, partly in section, of a direction couplingdevice utilizing nonreciprocal iield displacement, operation of which isbased upon use of an element of a composition herein;

FIG. 8 is a perspective view, partly in section, of a device having agarnet-loaded resonance cavity; and

FIG. 9 is a perspective view, partly in section, of a garnet-loaded,nonreciprocal attenuating device employing a balanced wire linetransmission system.

It is well known that the effective gyromagnetic ratio of a ferromagnetis given by the ratio of the net magnetization to the net angularmomentum,

in which the index z' denotes a particular magnetic sublattice, Mirepresents the magnetization, and 'y1 is the gyromagnetic ratio of theith sublattice. Since the individual sublattice magnetizations areeither parallel or antiparallel to the net magnetization, it is possibleto obtain materials for which the net angular momentum XM1/'yb is nearlyzero, and weft, the effective gyromagnetic ratio, is very large. Thesematerials are obtained by selective substitution of nonmagnetic ions formagnetic ions, This technique is known as angular momentum compensationand is described, for example, in Microwave Ferrites and Ferrimagnetics,Lax and Button, McGraw-Hill Book Co.. Inc., 1962, pages 248, et seq.

While this technique has resulted in large gyromagnetic ratios in anumber of ferrimagnetic materials, they have always been accompanied byvery small saturation moments and by very broad ferromagnetic resonanceline widths. The practical advantage of such increased gyromagneticratios has, in this manner, been lost for rnost device applications. Thepresent invention derives from the discovery that angular momentumcompensation of europium-iron garnet by use of gallium providesferrimagnetic materials with large effective gyromagnetic ratios whichmanifest saturation moments and ferromagnetic resonance line widthsentirely suitable for device use.

Referring again to FIG. 1, it is seen that the saturation magnetization,41rMs, plotted in units of gauss, drops from a value of about 1300 forpure Eu3Fe5O12 to a compensation point at an x value of about 0.75. Forlarger amounts of .gallium, the moment increases, reaching a turnoverpoint for gallium inclusion of the order of 1.75 in the formula. Whilethe experimental apparatus utilized was not sensitive to momentdirection, theory, as substantiated by the slope of the magnetizationcurve before and after a value of x equals 0.75, suggests that thisvalue represents a true magnetic compensation point, and that theportion of the curve representing larger substitutions would properly bedrawn as extending into the fourth quadrant.

FIG. 2 is a plot showing the dependence of the gyromagnetic ratio on xin the formula. It is seen that this quantity, crucial to the deviceuses herein, peaks in absolute value at an x value of about `1.2 This isthe approximate angular momentum compensation point for the materials ofthis invention and represents the preferred composition. The specifiedrange of x values from 0.8 t-o 1.8 set forth above directly results fromstudy of data of the type here depicted. It is seen that these limitsdefine a compositional range manifesting hm! values of a minimum ofabout three. This characteristic, taken together with the narrow linewidth and other properties, defines a range of materials usefullyincorporated in the devices herein and in gyromagnetie `devices ingneral.

Study of FIG. 3, in conjunction with FIG. l, reveals the nature of thedependence of the effective anisotropy eld on composition. It is seenthat the values of the effective field over the compositional range ofconcern are within suitable limits for device appli-cations.

The waveguide configuration for frequency doubling shown in FIG. 4depends for its operation on cylindrical post 1, which is constructed ofa composition herein. This device, which is otherwise conventional,provides for the introduction of vertically polarized electromagneticwaves 2 into guide 3 and for exiting of horizontally polarizedelectromagnetic energy at end 4. Structure 5, which restricts thedimension corresponding with the direction of the H vector of the outputenergy, acts as a cutoff for the frequency-doubled output. Structure `6serves a similar function for the input energy in restricting thehorizontal dimension corresponding with the H vector for the input, soas to prevent its exiting together with the desired output. Structure 7is an adjustable phase shifter which, by effectively increasing ordecreasing the dielectric constant for frequency-doubled energy, permitsthe attainment of an optimum constant and, consequently, thereinforcement of output by any frequency-doubled waves which have beenrejected by structure 5.

In FIG. 5, rectangular waveguides 11 and 12 are tapered smoothly into acircular waveguide 13. The rectangular waveguides 14 and 15 are joinedto the circular waveguide 13 near a rectangular guide 11 at the lefthandend, and near a rectangular guide. 12 at the righthand end,respectively. If imaginary planes be passed through each of the fourrectangular waveguides 11, 12, 14, and 15, parallel to the longestdimension of the rectangular section, the positioning of the guides 11and 14 will be such that the planes mentioned above for this pair ofguides will intersect perpendicularly. Similarly, the guides 12 and 15are set at right an-gles to one another at the right-hand end p of thedrawing shown. The planes passing through the guides 11 and 12 are,further, inclined to one another at an angle of 45 degrees, and thewaveguides 14 and 15 are similarly relatively inclined at an angle of 45degrees.

In sum, there are two pairs of guides, 11 and 14, and 12 and 15, themembers within a pair being disposed at right angles. Both members ofone pair, say waveguide 12 and waveguide 15, are rotated 45 degrees withrespect to the members of the rst pair, however, so that for any memberof either of the two pairs of perpendicular waveguides there is acorresponding member of the other perpendicular pair inclined to thefirst member at an angle of 45 degrees.

Within the circular waveguide 13 is a pencil 16 of the garnet materialsconsidered herein, mounted in a nonmagnetic dielectric material 17, suchas, for example, polystyrene foam. Surroundingr the garnet pencil 16,enclosed in the circular waveguide 13, is a magnetic source 18, such asan electromagnet or permanent magnet, capable of producing alongitudinal magnetic field.

In a magnetic field, a -garnet element has the property of rotating theplane of polarization of an incident plane polarized wave. The rotationproduced in the element 16 shown, for example, is determined by thenature of the garnet used, by the dimensions of the garnet element 16,and, in addition, by the strength of the magnetizing field from thefield source 18, and by the specific geometry of the waveguide 13 andthe mounting of the element 16 therein. The sense of the Faradayrotation is deterined by the direction of the magnetizing field.

In the circulator shown in FIG. 5, for example, the length of theelement 16 and the strength and direction of the magnetizing field fromthe source 18 may be chosen to give a 45-degree counterclockwiserotation viewed from n to p, in FIG. 5, for waves passing through theelement 16 from n to p. In passing from p to n, waves are rotated in thesame sense by the garnet.

Thus, waves electrically polarized perpendicular to the longestdimension of the rectangular section of the waveguide 11 pass the guide14 and penetrate the garnet 16. As the geometry of the guide 14 is suchas to transmit only waves polarized perpendicularly to those entering at11, the waves entering 11 are unaffected by passing the guide 14. In thegarnet, a 4 5-degree counterclockwise rotation results, and the waveplane is oriented for transmission out through guide 12. Again, theoutgoing wave is unaffected by the guide 15 set at right angles to theplane of the polarized wave in guide 12. If a wave enters the guide 12,reversing the direction of transmission in the original illustration, itpasses guide 15, is rotated by the garnet in the same sense as before,and is thus, this time, oriented for transmission through the guide 14.By similar considerations, waves entering guide 14 are made to exitthrough the guide 15;` and waves entering the guide 15 leave, afterrotation, by waveguide 11.

A more detailed explanation of the device described above is to `befound in U.S. Patent 2,748,352, issued to S. E. Miller.

FIG. 6 shows a Faraday rotation device comprising a garnet loading 21 ina round dielectric waveguide 22. The garnet 21 comprises the materialsconsidered later herein, and the waveguide 22 may consist of anydielectric material having a dielectric constant materially differentfrom that of air, such as, specifically, polystyrene or polyethylene.

Electromagnetic Waves are transmitted through dielectric media similarto that used in the construction of the waveguide 22 without aconductive shield surrounding the transmitting medium. The wave isguided by the dielectric, with a portion of the energy conducted in afield surrounding the rod. By joining the dielectric rod 22 with thegarnet segment 21, a portion of the wave energy can be led through theferromagnetic material and can be thereby affected. As in FIG. 5,permanent magnets or electromagnets, not shown, are used to produce ahorizontal magnetic field in the region of the garnet and rotation ofthe wave traversing the garnet is effected. Tapered portions 24 of thedielectric rod 22 fit into conical hollows in the garnet rod 21 toassure matching and to minimize possible radiation loss. An additionalcylindrical cover 23 of dielectric material is provided over the garnetsegment to aid in maintaining a constant energy field which f mightotherwise be disrupted by disparity between the indices of refraction ofthe garnet material 21 and the dielectric 22.

In operation, a linearlyr polarized wave, for example, introduced at sinto the waveguide 22 is propagated through the garnet 21 and emerges att with a rotation in the angle of polarization. Means, not shown, may beprovided for utilizing the rotation observed in the construction of acirculator, as in FIG. 5, or the segment of the circuit shown in FIG. 6may lbe adapted to other purposes.

A complete and detailed explanation of devices employing garnet-loadeddielectric waveguides is to be found in U.S. Patent 2,787,765, issued toA. G. Fox.

FIG. 7 shows a multibranch network in which gyromagnetic materials areused to create field displacement effects. Shown are two rectangularmetal waveguides 31 and 32. The guide 31 is placed with one narrow wallcontiguous to a wide wall of the guide 32, and is so located as to lieoff the center line of said guide 32. Apertures 33, extending throughthe contiguous Walls of the guides 31 5, and 32, are used to couple theguides 31 and 32 electromagnetically. These apertures, lying on thecenter line of the narrow wall of the guide 31, are displaced, as is theguide 31 itself, from the center line of the guide 32.

Within the guide 32, and in the region of the coupling apertures 33, aremeans for producing a non-reciprocal displacement of the magnetic fieldpattern therein, comprising, in this case, two slabs 34 of a garnetmaterial as later described herein. Means, not shown, such as a solenoidor permanent magnet, are provided for creating a uniform magnetic fieldin each of the garnet slabs 34, so that said slabs are magneticallypolarized at right angles to the direction of propagation of wave energyin the waveguide 32. Both slabs 34 are polarized in the same direction.

In a rectangular waveguide such as that shown in FIG. 6 as 32, themagnetic field of a dominant mode wave being propagated through thewaveguide will be such that a clockwise-rotating and acounterclockwise-rotating component of the magnetic intensity will befound respectively at one or the other extremity of the longestrectangular dimension of the waveguide wall. That is, depending on thedirection of wave propagation, the direction of the polarization at oneof the waveguide walls will be clockwise or counterclockwise, withrotation in the opposite sense being found in the magnetic intensity atthe other wall for a given direction of wave propagation. Upon reversingthe direction of propagation, the sense of the polarization at each wallalso reverses.

By biasing the garnet loadings 34 in a magnetic field perpendicular tothe length of the waveguide 32, as previously mentioned, each elementbeing polarized in the same direction, the electron spins and associatedmoments within the garnet can be caused to precess about the line of thebiasing magnetic Ifield on the garnet, producing a magnetic momentrotating in a plane normal to the biasing field, or, that is, in theplane of the magnetic component of the waves propagated along thewaveguide 32. The rotating moment produced by electron spin in thegarnet will correspond, on one side of the waveguide or the other, tothe rotating component of the magnetic intensity of the wave, resultingin a permeability less than unity for one of the garnet strips 34. Onthe other side of the waveguide 32, the 'biasing field producedprecession with a moment in a sense opposite to the rotating componentof the waves magnetic field, resulting in a permeability greater thanunity for this second garnet strip.

The discrepancy in permeability for the two strips 34 results in adisplacement of the normal eld pattern. Without the biasing magneticfield applied to the garnet slabs 34, the magnetic field intensity ofthe propagated wave in the waveguide 32 is null along the center line ofthe waveguide, rising to a maximum at the sides of the guide. When abiasing field is applied to the garnet, the eld pattern of the wave maybe distorted to give a null value in the region immediately beneath theoff-center coupling apertures 33. No coupling results in this case.Reversing the direction of wave propagation in the waveguide 32, withoutchanging the direction of the bias on the garnet elements 34, willresult in a displacement of the null field area to a point on the otherside of the center line of the waveguide 32, away from the couplingapertures 33. Coupling of the guides 31 and 32 will result for thisdirection of wave propagation.

Thus, for one direction of propagation through the waveguide 32,coupling with the guide 31 results, while reversing the propagationdirection will produce no coupling with the guide 31.

A more detailed explanation of the device discussed above, and otherfield-displacement devices, is to be found in U.S. Patent 2,849,683,issued to S. E. Miller.

FIG. 8 is a perspective view, partly in section, of waveguide structurescoupled by a chamber containing a gyromagnetic garnet element to producea three-branch circulator.

In the drawing, a hollow rectangular waveguide 41 is abutted by a secondwaveguide 42 of a type capable of supporting circularly polarized waves.The guide 42 is tapered smoothly into a rectangular waveguide 43 whichwill transmit linearly polarized waves only. Means, such as positionedmetal fins 73 and 74, are so disposed at the junction of waveguides 42and 43 as to interconvert circularly polarized waves in guide 42 to andfrom linearly polarized waves in guide 43, by introducing a -degreephase shift in selected components of the impinging waves.

A resonant cavity 48 is formed in the lower portion of the waveguide 42,said cavity being bounded at the top by a perforated reactive diaphragm47 and at the bottom by the waveguide 41. The diaphragm 47 is sopositioned as to render the length of the cavity 48 a multiple ofonehalf of the guide wavelength of the waves to be transmittedtherethrough. Apertures 45 and 46 couple wave energy to and from guides41 and 42 and guides 42 and 43, respectively.

The aperture 4S is of such geometry and is so positioned, by techniquesknown to those skilled in the art, relative to the waveguides 42 and 41,that for waves transmitted through waveguide 41 from u to w in thediagram, a circularly polarized wave will be introduced into the cavity48, while for those waves transmitted through the guide 41 from w to u,a wave circularly polarized in the opposite sense will be found in thecavity 48.

Within said cavity 48 is mounted an element 49 of a gyromagnetic garnetof the kind later considered herein. The garnet 49 is mounted in amaterial 71 of low dielectric constant, such as polyfoam Surrounding thecavity 48 in which the garnet 49 is located are means 72, such assolenoidal winding, for producing a steady polarizing magnetic fieldparallel to the direction of wave propagation in the waveguide 42.

In a gyromagnetic garnet similar to that of the element 49 in thedrawing, polarized by a biasing magnetic field, the permeabilitypresented to circularly polarized waves transmitted therethrough isdifferent for waves polarized in opposite senses, as earlier mentioned.When the sense of the wave polarization is coincident with the sense ofthe rotating magnetic moment associated with the precession of electronspins in the garnet, the permeability of the garnet has a value aboveunity. When the senses of the wave and the moment in the ferrite areopposite, the permeability of the garnet is less than unity for biasingfields insutiicient to produce resonance in the garnet. Depending on thestrength of the field, further, the garnet permeability may take valuesless than zero.

The circulator shown in FIG. 8 employs this gyromagnetic property of thegarnet element 49 in its operation. For illustration, let the positionof the aperture 45 be such as to produce a counterclockwise polarizedwave in waveguide 42 when a wave is transmitted along guide 41 from u tow. Further, let the biasing field from the source 72 be in a directionas to permit transmission of such a polarized wave through the garnetelement 49 in the cavity 48. When the cavity 48 is made of a lengthwhich is a multiple of the half wavelength of the transmitted wave, bypositioning of the diaphragm 47, the cavity 48 is resonant for the wave,and the wave, after conversion by the fins 73 and 74 appears as alinearly polarized wave at v.

A wave transmitted in waveguide 41 from w to u, however, will beclockwise polarized in waveguide 42, in this example. The biasing fieldon the ferrite 49 produces a low permeability for such a wave, and noresonance or transmission of terminal v ensues. Waves introduced at w,thus, emanate only at u.

The introduction of wave energy at v results, for the position of thefins 73 and 74 chosen, in the introduction of a counterclockwiserotation. Such a wave, as seen earlier, will be resonant in the cavity48, and will be coupled into the waveguide 41. Passage through theaperture 45 by such a counterclockwise polarized wave will result in awave, the magnetic components of which are characteristic of waves beingtransmitted from u to w in the example under discussion, and emergenceof the wave at w will result. By adjustment of the size of the apertures45 and 46, the impedances of the terminals u, v, and w, which terminalsare coupled by the apertures through the cavity 48, can be matched as togive transmission without reliection along the paths u to v, v to w, andw to u, so that the element pictured is a nonreciprocal circulator.

In FG. 9 is shown a millimeter wave circuit element, which may be usedas an isolator, suitable for connection directly into a two-wirebalanced line transmission system. The embodiment 4pictured comprisestwo pairs of parallel conductors 51, 52, 53, and S4, equally spaced andsymmetrically aligned relative to each other. The conductors are bridgedin pairs by connecting elements 55, 56, 57, and 58.

Thin discoid dielectric spacers 81 through 84 are longitudinally placedyalong the line to support the conductors in their above-describedrelationship. Spacers 82 and 83, in addition, may serve to support agyromagnetic garnet body 59 comprising materials of the type hereinlater described. A shield 86 serves to support the structure andprotects the conductors 51 through 54 from external mechanical andelectrical iniuences. A longitudinal magnetic field is supplied by awinding 85 to polarize the ferrite 59. Control of the energizing fieldis provided so that strengths sufficient to produce a ferromagneticresonance condition in the garnet 59 may be produced if desired.

Loading vanes 88 and 89 are disposed, respectively, between the wirepairs 51 and 53 at the right-hand end of the circuit element shown, 'andbetween the pairs 52 and 54 at the left-hand end. The vanes, of amaterial having a high dielectric constant, extend longitudinallybetween the wire pairs mentioned for a length sufficient to introduce a90-degree delay in a voltage between the conductors comprising a pair.

When .a voltage, balanced with respect to ground, is applied between thebridges 55 and 56, the voltage between conductors S4 and 53 is delayed90 degrees by the vane 88. Similarly, a 90-degree shift in voltagebetween the lines 52 and 51 is produced by the dielectric material 88.In consequence, a circularly polarized wave is produced by the four-wiresystem in the region of the garnet loading 59. Upon passing the loading59, the vane 89 reintroduces 90-degree voltage delays in the conductors,

in a fashion similar to the operation of the vane 88, so

that a balanced voltage is again applied to the load on the far side ofthe garnet body 59.

lf the rotation produced in the polarized wave in the region of thegarnet 59 is similar in sense to the precesaion of electron spins andthe moment associated therewith in the garnet, the wave is transmittedalmost unaffected by the conductors 51 through 54 from the source to thecircuit load. If the polarized wave rotates in -a sense opposite to therotating magnetic component generated in the garnet 59, however, almostno transmission past the garnet is observed when the garnet is excitedto its resonant frequency by the magnetic source 85. Since attemptedtransmission in opposite directions through a circuit element such asthat shown in FIG. 9 will produce waves polarized in opposite senses inthe supporting conductors 51 through 54, the element shown may `be usedas an isolator, permitting transmission in one direction only, when thegarnet biasing field is maintained in a constant direction and at astrength producing ferromagnetic resonance condition in the garnetmaterial 59.

A more complete and detailed description of the balanced wiretransmission system described above, and others, is to be found in U.S.Patent 2,892,161, issued to A. M. Clogston, and assigned to the assigneeof this application.

Workers in the art are familiar with v-arious techniques for growth ofgarnet compositions, all of which are applicable to these compositions.For most of the uses described, particularly where the devices are to beutilized in the high frequency ranges, .for which these materials areparticularly suitable, single crystals are preferred or are evennecessary. Suitable growth techniques include the various types ofrandom nucleation. Fluxes that may be utilized include the lead oxide ofI. W. Nielson U.S. Patent 2,957,827, the lead oxide-lead fluoride fluxof I. W. Nielsen U.S. Patent 3,050,407, and the lead oxideboron oxideflux of 1.1. Remeik-a U.S. Patent 3,079,240, all of which patents areassigned to applicants assignee. Seeded growth using the same fluxes orothers, fiame fusion, and crystal pulling may result in larger singlecrystalline sections where such are required.

Many of the results reported herein resulted from measurements made oncrystals grown in lead oxide-boron oxide. The general process utilizedin the growth of crystais from this liux is set forth in detail in U.S.Patent 3,079,240 at column 2, line 20, et seq.

The following is a tabulation of eight garnet compositions herein. Thistable contains four columns, the first of which designates examplenumber; the second, the value of x in the formula; the third, thestarting amount of gallium in terms of grams of gallium oxide, Ga2O3;and the fourth, the starting amount of iron oxide, Fe2O3, again ingrams. The amount of europium oxide, Eu2O3, was 16 grams for each ofExamples l through 6. Measured 'ym values for these compositions rangefrom a minimum of about 6 up to 30 or greater.

Example x G2120; Felt);

(in grams) (in grams) (in grams) The invention has necessarily beendescribed in terms of a limited number of embodiments. From acompositional standpoint, the invention has been traced tocharacteristics of the pure system Eu3GaxFe5 xO12, in which x equalsfrom 0.8 to 1.8. It is well known that magnetic garnet compositions maycontain additional ingredients, either as unintentional impurities orIas intentional inclusions. For the purposes herein, it is consideredthat unintentional inclusions should be limited to a maximum of theorder of one percent, with the line broadening impurities, manganese,silicon, cobalt and the rare earths being kept to total content of amaximum of 0.1 percent. Intentionally added ingredients should generallybe restricted to partial substitutions for europium, usually for thepurpose of tailoring magnetic moment, and should not exceed 30 percentof the europium in the formula on an atomic basis.

The invention generally derives from the discovery that Ga3+ ionsmanifest an unusually strong preference for tetrahedral sites ineuropium-iron garnet not seen in other lattices, for example anyttrium-iron garnet or for other ions in other systems. This, in turn,results in an angular momentum compensation point for an appreciablesaturation moment. Compositions at and about the angular momentumcompensation. point defined above manifest unusually high effectivegyromagnetic ratios, so permitting operation of harmonic generators,isolators, and other -related devices at higher frequencies for givenapplied magnetic fields. Variations on the devices shown and a host ofdevices not shown, operation of which may beneficially share theadvantages set forth, are known to those skilled in the art. All suchvariations are to be considered within the scope of this invention.

What is claimed is:

1. A microwave component having a g value of at least four (4) andconsisting essentially of l EU3G3XF5 XO12 in which x equals from 0.8 to1.8.

2. Component of claim 1, in which x equals approximately 1.20.

3. A microwave component having a g value of at least four (4) andcomprising a single crystal of the cornposition Eu3GaXFe5 XO12, in whichx represents from 0.8 to 1.8, together with means for introducing andextracting electromagnetic energy.

4. Component of claim 3, in which the said electromagnetic energy issubstantially plane polarized.

S. Component of claim 4, in which the extracted energy is a harmonic ofthe introduced energy, and in which the said means comprise guidesections, the major axes of which are normal to each other.

6. A microwave component having a g value of at least four (4) andcomprising at least one waveguide and a gyromagnetic garnet body of acomposition comprising Eu3GaXFe5 xO12, in which x equals from 0.8 to1.8.

7. Component of claim 6, together with means for subjecting the saidbody to electromagnetic energy of a frequency of at least 50 gigacyclesper second.

References Cited UNITED STATES PATENTS 2,748,352 5/1956 Miller 333-142,849,683 8/1958 Miller S33- 1.1 2,892,161 6/1959 Clogston S33- 24.22,922,876 1/1960 Ayres et al 333-24.1 2,93 8,183 5/1960 Dillon.

3,079,240 2/ 1963 Remeika.

3,164,768 1/1965 Stiglitz et a1. 321-69 3,229,193 1/ 1966Schaug-Pettersen et al. 321-69 3,260,852 7/1966 Hetter 307-883 OHN F.COUCH, Primary Eaxmner.

G. GOLDBERG, Assistant Examiner.

6. A MICROWAVE COMPARTMENT HAVING A G VALUE OF AT LEAST FOUR (4) ANDCOMPRISING AT LEAST ONE WAVEGUIDE AND A GYROMAGNETIC GARNET BODY OF ACOMPOSISTION COMPRISING EU3GAXFE5-O12, IN WHICH X EQUALS FROM 0.8 TO1.8.